1. Field of the Invention
This invention relates to a modified polyolefin resin and a composition containing the same.
Polyolefins modified with polymerizable monomers having in their molecules a polar group such as unsaturated carboxylic acid and its derivatives have been widely used for imparting adhesive property, dying property, and miscibility with other resins to those polyolefins which are primarily non-polar, hence no adhesive property and compatibility with other polar substances, and for producing a composite material by blending such polyolefins and other substances. For instance, such modified polyolefins are used for the manufacture of a multi-layered film and sheet in the form of a laminated product with metals or polar resins (such as polyamide, polyester, copolymer of ethylene and vinyl alcohol, polyvinyl halide, and so forth). Besides this, the modified polyolefins are also used for adhesion between a coated protective layer and a metal constituting a metal shaped article. Further, such polyolefin per se or a composition containing the same in it is used for obtaining a composition having good dispersibility and excellent mechanical strength, with increased compatibility and adhesivity between filler, pigment, etc. and the matrix resin. In certain other cases, the modified polyolefin per se is present in the matrix resin in a state of its being in a favorable dispersion to thereby improve impact resistance and other properties of the matrix resin.
The present invention is directed to the modified polyolefin resin capable of being widely used in such use, and, in particular, to a resin composition effective for manufacture of a composite film or sheet.
2. Description of Prior Arts
The technique of modifying an ethylene type copolymer containing ethylene as the principal constituent (hereinafter abbreviated as "polyethylene") with a polar monomer has been well known. Above all, polyethylene which has been modified with unsaturated carboxylic acid or its anhydride possesses good adhesion with metal, epoxy resin, and so forth, hence it is used for a metal pipe coating, etc., and moreover such modified polyethylene is capable of producing a composite of a high barrier resin by joining a composite film or sheet composed of the ethylene type resin with nylon, ethylene and vinyl alcohol copolymer, polycarbonate resin, polyethylene terephthalate, aluminum foil, etc., on account of which it has been widely used as the food packing material.
There are several kinds of polyethylene used for modified polyethylene such as high pressure method, low density polyethylene (.rho.=0.915 to 0.930 g/cm.sup.3), medium or low pressure method, high density polyethylene (.rho.&gt;0.94 g/cm.sup.3), medium or low pressure method, medium density polyethylene (.rho.=0.93 to 0.95 g/cm.sup.3), and so forth. A linear copolymer of much lower density is disclosed in, for example, Japanese Unexamined Patent Publication No. 165413/1982, which is directed to a metal laminate body using a linear, low density polyethylene having a density of 0.915 to 0.935 g/cm.sup.3 (which will hereinafter be abbreviated as "LLDPE").
According to that invention, use of LLDPE would contribute to improve the adhesive strength and the stress-cracking resistance of the resin composition. However, while the resin composition to be obtained with use of LLDPE might be superior in its adhesive strength and the stress-cracking resistant property to the resin composition with the conventional medium or low pressure method, high density polyethylene and high pressure method, low density polyethylene as the base material, it must be said that such resin composition still falls short of its adhesive strength and heat-sealing property at the time of high speed molding of the resin composition, which is the principal performance to be the gist of the present invention.
Further, Japanese Unexamined Patent Publication No. 170940/1982 discloses a modified polyethylene using a medium or low pressure method ethylene copolymer having a density of from 0.900 to 0.940 g/cm.sup.3. In the examples of this Japanese Unexamined Patent Publication, however, there is only description of an example of the modified polyethylene having a density in a range of from 0.920 to 0.925 g/cm.sup.3, and nothing is said about the effect to be derived from the characteristics of the polyethylene according to the present invention with the exception of the description such that, when used for coating of metal material, such modified polyethylene provides excellent durability in adhesion (such as resistance to warm water, resistance to stress-cracking, and so forth).
Furthermore, as a copolymer having a much lower density, there has been known a modified resin obtained by modification of a copolymer of ethylene and .alpha.-olefin with a low degree of crystallization in a range of from 30% to a few percent (.rho.=0.86 to 0.88 g/cm.sup.3) and a copolymer rubber of ethylene and .alpha.-olefin (.rho.=0.86 to 0.87 g/cm.sup.3) of much lower density. For example, Japanese Unexamined Patent Publication No. 82/1979 discloses a blend of a modified polymer obtained by grafting maleic anhydride on a copolymer of ethylene and .alpha.-olefin having a degree of crystallization of 30% or below and a crystalline polyolefin resin. However, examples in this Unexamined Japanese Patent Publication disclose only a copolymer having a density of not reaching 0.89 g/cm.sup.3 (which is expressed in terms of a comonomer composition), but not a single description can be seen in it as to the effect to be derived from definition of the physical properties that can be expressed by a value of a product of melt tension and melt-index of the polymer material. Besides this, there have been proposed various techniques of blending an unmodified rubbery copolymer and a modified substance of a crystalline polyolefin, and so on, although no use has ever been made of a polymer having the density and the characteristics as that of the present invention.
Possibility of obtaining a copolymer having a density of from 0.890 to 0.910 g/cm.sup.3 by copolymerization of ethylene and .alpha.-olefin has been known per se. This technique, however, has not been put into practice upto recent years, because of various difficulties to be overcome for the purpose of its production in an industrialized scale, such as manner of handling the polymer (in particular, agglutination of polymer particles), increase in components soluble in solvent, and others. In recent years, such industrialized production has become feasible owing to improvement in the slurry polymerization method or improvement in the gas-phase polymerization method.